The following important events in the history of Colorado affected political boundaries, record keeping, and family movements.

1803	The United States acquired the sections of Colorado north and east of the Arkansas River as part of the Louisiana Purchase. Beginning in 1806 government expeditions were sent to map the area, and fur trappers and traders followed in the 1820s. Western settlers in the 1840s and 1850s bypassed Colorado on their way to the Pacific Coast.
1848	The United States acquired the rest of present-day Colorado from Mexico.
1851	Hispanic families from New Mexico founded San Luis, the oldest continually occupied town in Colorado.
1854	The Colorado area was divided politically among the territories of Kansas, Nebraska, Utah, and New Mexico.
1858	Denver and other mining towns were organized by Colorado's early gold seekers. In 1858 the miners also organized Arapahoe County of Kansas Territory.
1859	Colorado pioneers created what they called Jefferson Territory without the sanction of Congress. It was to have included all of present-day Colorado and some areas of Utah and Wyoming.
1861	Congress organized the Colorado Territory. The first seventeen counties were organized the same year.
1870	Railroad links between Denver and Cheyenne and between Denver and Kansas City connected Colorado with the east and west coasts.
1876	Colorado became a state.
1881	Western Colorado was officially opened to white settlement after most of the Ute Indians had been moved to reservations in Utah.
1890	Colorado's population exceeded 400,000 when the last major gold strike was made at Cripple Creek.